Corrosion inhibitors

ABSTRACT

Melamine derivatives and mixtures thereof with aqueous systems, a process for inhibiting corrosion of metals and metal alloys with melamine derivatives and mixtures thereof and the use of melamine derivatives and mixtures thereof as corrosion inhibitors for aqueous systems, for example water/oil mixtures, especially in the field of cleaning compositions, cooling fluids, oilfield chemicals or lubricants.

The present invention relates to the use of specific compounds, especially melamine derivatives, as corrosion inhibitors for aqueous systems, for example water/oil mixtures, especially in the field of cleaning compositions, cooling fluids, oilfield chemicals or lubricants. In addition, the invention also relates to specific compounds, especially melamine derivatives, and mixtures thereof with aqueous systems, for example water/oil mixtures. The invention further provides a process for inhibiting the corrosion of metals or metal alloys.

Further embodiments of the present invention can be inferred from the claims, the description and the examples. It will be appreciated that the features of the inventive subject matter which have been specified above and are still to be explained below can be used not just in the specific combination stated in each case but also in other combinations without leaving the scope of the invention. Preference and particular preference is given to the embodiments of the present invention in which all features have, respectively, the preferred and particularly preferred definitions.

The corrosion of metals or metal alloys, especially the corrosion of these materials in contact with solutions or mixtures comprising water, is a constant challenge in such different fields of industry as the cleaning of metal surfaces, the reliable operation of cooling circuits, the production of oil or the lubrication of moving metal parts, for example in engines.

Frequently, the technical solution proposed for the corrosion problem in such systems is the addition of corrosion inhibitors.

EP 0 046 139 A1 describes processes for inhibiting the corrosion of iron or ferrous metals in contact with aqueous systems by addition of particular triazine carboxylic aids or water-soluble salts thereof as a corrosion inhibitor.

DE 196 48 843 A1 describes melamine polycarboxamides and use thereof for inhibition of the corrosion of iron or ferrous metals in contact with aqueous systems.

EP 0 553 962 A1 discloses a composition for inhibiting corrosion, comprising carboxylic acids based on triazine compounds and sulfonamide compounds and dicarboxylic acids.

EP 0 682 022 A2 describes compounds which comprise triazine and (benzo)triazole radicals and have corrosion-inhibiting properties.

In the prior art processes, however, the efficacy of corrosion inhibitors frequently depends on specific boundary conditions in the respective system, for example the pH or a specific composition of the metal or metal alloy.

It was therefore an object of the present invention to provide corrosion inhibitors, the use of which in processes for inhibiting the corrosion of metals or metal alloys is very substantially independent of the boundary conditions such as the pH or the composition of the metal or metal alloy.

This object is achieved by the various subjects and embodiments of the present invention, more particularly by the use of compounds of the general formula (I)

-   -   where     -   A¹, A², A³ are the same or different and are each independently         N—R¹¹, N—R¹², N—R¹³, S, O,         -   preferably N—R¹¹, N—R¹², N—R¹³, S,         -   more preferably N—R¹¹, N—R¹², N—R¹³,     -   R¹¹, R¹², R¹³ are the same or different and are each         independently H, C₁-C₂₀-alkyl, C₃-C₁₅-cycloalkyl,         -   preferably H, C₁-C₁₀-alkyl,         -   more preferably H, C₁-C₈-alkyl,     -   X¹², X²², X³² are the same or different and are each         independently (X-a) to (X-m) groups

-   -   * in the (X-a) to (X-m) groups denotes the bond to A¹, A² or A³,     -   ** in the (X-a) to (X-m) groups denotes the bond to Y¹², Y²² or         Y³²,     -   R⁴ is the same or different and is independently H, CH₃,     -   R⁵ is selected from the side chains of the natural alpha-amino         acids,         -   preferably —CH₃ (cf. alanine), —CH₂CH₂CH₂NH—C(NH)NH₂ (cf.             arginine), —CH₂CONH₂ (cf. asparagine), —CH₂COOH (cf.             aspartic acid), —CH₂SH (cf. cysteine), —CH₂CH₂CONH₂ (cf.             glutamine), —CH₂CH₂COOH (cf. glutamic acid), —H (cf.             glycine), —CH₂(C₃H₃N₂) (cf. histidine), —CH(CH₃)CH₂CH₃ (cf.             isoleucine), —CH₂CH(CH₃)₂ (cf. leucine), —CH₂CH₂CH₂CH₂NH₂             (cf. lysine), —CH₂CH₂SCH₃ (cf. methionine), —CH₂(C₆H₅) (cf.             phenylanaline), —CH₂CH₂CH₂— (cf. proline), —CH₂OH (cf.             serine), —CH(OH)CH₃ (cf. threonine), —CH₂(C₈H₆N) (cf.             tryptophan), —CH₂(C₆H₄)OH (cf. tyrosine), —CH(CH₃)₂ (cf.             valine),         -   more preferably —CH₃, —CH₂CH₂CH₂NH—C(NH)NH₂, —CH₂CONH₂,             —CH₂COOH, —CH₂CH₂CONH₂, —CH₂CH₂COOH, —H, —CH₂(C₃H₃N₂),             —CH(CH₃)CH₂CH₃, —CH₂CH(CH₃)₂, —CH₂CH₂CH₂CH₂NH₂, —CH₂(C₆H₅),             —CH₂CH₂CH₂—, —CH(OH)CH₃, —CH₂(C₆H₄)OH, —CH(CH₃)₂,     -   Y¹², Y²², Y³² are the same or different and are each         independently carboxylate, phosphate, phosphonate, sulfonate,         quaternary ammonium group,         -   preferably COOH, PO(OH), PO(OH)₂, SO₃H,         -   more preferably COOH, PO(OH)₂,     -   X¹²-Y¹²,     -   X²²-Y²²,     -   X³²-Y³² may be the same or different and may each independently         also together be O—H,     -   n, m, are the same or different and are each independently an         integer from the range from 1 to 20, preferably from 1 to 10,         especially from 1 to 6,     -   p is an integer from the range from 1 to 30, preferably from 1         to 10,     -   or of salts of the compounds of the general formula (I),         obtainable by at least partial neutralization with a base         selected from alkali metal hydroxides and amines, preferably         amines, more preferably monoethanolamine, triethanolamine,         tridecylamine,     -   where the substituents R¹¹, R¹² and R¹³ may each be interrupted         at any position by one or more heteroatoms, in which case the         number of these heteroatoms is not more than 10, preferably not         more than 8, even more preferably not more than 5 and especially         not more than 3, and/or may each be substituted at any position,         but not more than five times, preferably not more than four         times and more preferably not more than three times, by         C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, where         these may likewise be substituted not more than twice,         preferably not more than once, by the groups mentioned,     -   as corrosion inhibitors for aqueous systems, for example         water/oil mixtures, in contact with metals or metal alloys.

Heteroatoms are phosphorus, oxygen, nitrogen or sulfur, preferably oxygen, nitrogen or sulfur, any free valences of which are satisfied by H or C₁-C₂₀-alkyl.

Specifically, the collective terms specified for the various substituents are defined as follows:

C₁-C₂₀-Alkyl: straight-chain or branched hydrocarbyl radicals having up to 20 carbon atoms, for example C₁-C₁₀-alkyl or C₁₁-C₂₀-alkyl, preferably C₁-C₁₀-alkyl, for example C₁-C₃-alkyl such as methyl, ethyl, propyl, isopropyl, or C₄-C₆-alkyl, n-butyl, sec-butyl, tert-butyl, 1,1-dimethylethyl, pentyl, 2-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, hexyl, 2-methylpentyl, 3-methyl-pentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, or C₇-C₁₀-alkyl such as heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, 1,1,3,3-tetramethylbutyl, nonyl or decyl, and isomers thereof.

C₃-C₁₅-Cycloalkyl: monocyclic saturated hydrocarbyl groups having 3 up to 15 carbon ring members, preferably C₃-C₈-cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl or cyclooctyl, and a saturated or unsaturated cyclic system, for example norbornyl or norbenzyl.

Aqueous systems in the context of the present application are understood to mean a mixture comprising water. This mixture is generally liquid under the use conditions of the aqueous system. Also covered here are mixtures having a very high or very low water content. For example, the water content in the aqueous system may be from 1 ppm to 1% by weight, based on the total amount of all substances in the aqueous system, the systems frequently being oil-based systems which have absorbed traces of water. In addition, the water content in the aqueous system may, for example, also be from 50 to 99.99999% by weight, based on the total amount of all substances in the aqueous system, in which case the systems are frequently those comprising predominantly water as a solvent or dispersant. Water/oil mixtures, for example water-in-oil or oil-in-water emulsions, are known to the person skilled in the art from his or her general specialist knowledge and are likewise aqueous systems in the context of the present invention.

The solubility of the compounds of the general formula (I) in the aqueous systems can advantageously be regulated via the degree of neutralization thereof. In addition, it is advantageously also possible to control the solubility of the compounds of the general formula (I) via the substituents, preferably via R¹¹, R¹², R¹³.

The compounds of the general formula (I) in the aqueous systems are present in molecularly dissolved form, in dispersed form or in suspended form.

The amount of the compounds of the general formula (I) used here may, for example depending on the respective end use, vary over a wide range, depending on the conditions in the aqueous system. Preference is given to from 0.001 to 5% by weight of the compounds of the general formula (I), based on the total amount of all substances in the aqueous system, particularly preferably to from 0.05 to 1% by weight, especially from 0.1 to 1% by weight. It will be appreciated that the compounds of the general formula (I) may also be present in a higher concentration in the aqueous system and may be diluted further, for example, for use thereof in an aqueous system by addition of a further aqueous system or addition to a further aqueous system.

In the compounds of the general formula (I), the (X-I) groups may each independently have block structure and/or random monomer arrangements. The (X-I) groups preferably have block structure or a random monomer sequence. More preferably, all (X-I) groups are the same and have block structure.

In a preferred embodiment of the invention, compounds of the general formula (I) are used in the field of cleaning compositions, cooling fluids, oilfield chemicals, electronics chemicals or lubricants. Particular preference is given to using the compounds of the general formula (I) in acidic aqueous systems, for example at a pH of 6.9 to 0. Examples of such acidic aqueous systems are acidic detergents or oilfield chemicals. In addition, particular preference is also given to using the compounds of the general formula (I) in basic aqueous systems, for example at a pH of 7.1 to 14.

A particular advantage in the inventive use of the compounds of the general formula (I) is that the corrosion inhibitors known in the prior art generally enabled very good corrosion protection only in the case of particular acids, whereas the compounds of the general formula (I) provide very good corrosion protection for a multitude of different acids.

In a further preferred embodiment, the metals or metal alloys in the inventive use comprise iron. The metals or metal alloys more preferably comprise, as well as iron, also chromium, nickel, molybdenum, aluminum, copper and/or zinc, especially copper or aluminum. In addition, the metals or metal alloys preferably comprise steel alloys. Especially preferably, the metals or metal alloys comprise iron, chromium, nickel, molybdenum, aluminum, copper and/or zinc as main constituents, for example in an amount of 50 to 99.99999% by weight based on the total amount of metal or metal alloy. In a particularly preferred embodiment of the inventive use, the metal alloys are steel alloys.

The present invention further provides compounds of the general formula (II):

-   -   where     -   A⁴, A⁵, A⁶ are the same or different and are each independently         N—R⁴¹, N—R⁵¹, N—R⁶¹, O,         -   preferably N—R⁴¹, N—R⁵¹, N—R⁶¹,         -   more preferably N—R⁴¹, N—R⁵¹, N—R⁶¹,     -   R⁴¹, R⁵¹, R⁶¹ are the same or different and are each         independently H, C₁-C₂₀-alkyl, C₃-C₁₀-cycloalkyl,         -   preferably H, C₁-C₁₀-alkyl,         -   more preferably H, C₁-C₈-alkyl,     -   X⁴², X⁵², X⁶² are the same or different and are each         independently (X-a′) to (X-m′) groups

-   -   * in the (X-a′) to (X-m′) groups denotes the bond to A⁴, A⁵ or         A⁶,     -   ** in the (X-a′) to (X-m′) groups denotes the bond to Y⁴², Y⁵²         or Y⁶²,     -   R⁶ is the same or different and is independently H, CH₃,     -   R⁷ is selected from the side chains of the natural alpha-amino         acids,         -   preferably —CH₃ (cf. alanine), —CH₂CH₂CH₂NH—C(NH)NH₂ (cf.             arginine), —CH₂CONH₂ (cf. asparagine), —CH₂COOH (cf.             aspartic acid), —CH₂SH (cf. cysteine), —CH₂CH₂CONH₂ (cf.             glutamine), —CH₂CH₂COOH (cf. glutamic acid), —CH₂(C₃H₃N₂)             (cf. histidine), —CH(CH₃)CH₂CH₃ (cf. isoleucine),             —CH₂CH(CH₃)₂ (cf. leucine), —CH₂CH₂CH₂CH₂NH₂ (cf. lysine),             —CH₂CH₂SCH₃ (cf. methionine), —CH₂(C₆H₅) (cf.             phenylanaline), —CH₂CH₂CH₂—(cf. proline), —CH₂OH (cf.             serine), —CH(OH)CH₃ (cf. threonine), —CH₂(C₈H₆N) (cf.             tryptophan), —CH₂(C₆H₄)OH (cf. tyrosine), —CH(CH₃)₂ (cf.             valine),         -   more preferably —CH₃, —CH₂CH₂CH₂NH—C(NH)NH₂, —CH₂CONH₂,             —CH₂COOH, —CH₂CH₂CONH₂, —CH₂CH₂COOH, —CH₂(C₃H₃N₂),             —CH(CH₃)CH₂CH₃, —CH₂CH(CH₃)₂, —CH₂CH₂CH₂CH₂NH₂, —CH₂(C₆H₅),             —CH₂CH₂CH₂—, —CH(OH)CH₃, —CH₂(C₆H₄)OH, —CH(CH₃)₂,     -   Y⁴², Y⁵², Y⁶² are the same or different and are each         independently carboxylate, phosphate, phosphonate, sulfonate,         quaternary ammonium group,         -   preferably COOH, PO(OH), PO(OH)₂, SO₃H,         -   more preferably COOH, PO(OH)₂,     -   X⁴²-Y⁴²,     -   X⁵²-Y⁵²,     -   X⁶²-Y⁶² may be the same or different and may each independently         also together be O—H,     -   q, r, are the same or different and are each independently an         integer from the range from 1 to 20, preferably from 1 to 10,         especially from 1 to 6,     -   s is an integer from the range from 1 to 30, preferably from 1         to 10,     -   or of salts of the compounds of the general formula (I),         obtainable by at least partial neutralization with a base         selected from alkali metal hydroxides and amines, preferably         amines, more preferably monoethanolamine, triethanolamine,         tridecylamine,     -   where the substituents R⁴¹, R⁵¹ and R⁶¹ may each be interrupted         at any position by one or more heteroatoms, in which case the         number of these heteroatoms is not more than 10, preferably not         more than 8, even more preferably not more than 5 and especially         not more than 3, and/or may each be substituted at any position,         but not more than five times, preferably not more than four         times and more preferably not more than three times, by         C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, where         these may likewise be substituted not more than twice,         preferably not more than once, by the groups mentioned.

In the compounds of the general formula (II), the (X-I′) groups may each independently have block structure and/or random monomer arrangements. The (X-I′) groups preferably have block structure or a random monomer sequence. More preferably, all (X-I′) groups are the same and have block structure.

Particular preference is given to the compounds of the general formula (II)

-   -   where     -   A⁴, A⁵, A⁶ are each NH,     -   X⁴², X⁵², X⁶² are each

-   -   Y⁴², Y⁵², Y⁶² are the same or different and are each         independently a carboxylate, phosphate, phosphonate, sulfonate         group,         -   preferably COOH, PO(OH), PO(OH)₂,         -   more preferably COOH,     -   q is an integer from the range from 1 to 6, preferably from 3 to         6, especially 6,     -   r is an integer from the range from 1 to 6, preferably from 1 to         3, especially 1,     -   or salts of these compounds, obtainable by at least partial         neutralization with a base selected from alkali metal hydroxides         and amines, preferably amines, more preferably monoethanolamine,         triethanolamine, tridecylamine.

Particular preference is additionally given to the compounds of the general formula (II)

-   -   where     -   A⁴, A⁵, A⁶ are each NH,     -   X⁴², X⁵², X⁶² are each

-   -   Y⁴², Y⁵², Y⁶² are the same or different and are each         independently a carboxylate, phosphate, phosphonate, sulfonate         group,         -   preferably COOH, PO(OH), PO(OH)₂,         -   more preferably PO(OH)₂,     -   s1 is an integer from the range from 1 to 6, preferably from 2         to 4, especially 2,     -   s2 is an integer from the range from 1 to 6, preferably from 2         to 4, especially 2,     -   or salts of these compounds, obtainable by at least partial         neutralization with a base selected from alkali metal hydroxides         and amines, preferably amines, more preferably monoethanolamine,         triethanolamine, tridecylamine.

Particular preference is additionally given to the compounds of the general formula (II)

-   -   where     -   A⁴, A⁵, A⁶ are each NH,     -   X⁴², X⁵², X⁶² are each

-   -   R⁷ —CH₂CH₂SCH₃,     -   Y⁴², Y⁵², Y⁶² are the same or different and are each         independently a carboxylate, phosphate, phosphonate, sulfonate         group,         -   preferably COOH, PO(OH), PO(OH)₂,         -   more preferably COOH,     -   or salts of these compounds, obtainable by at least partial         neutralization with a base selected from alkali metal hydroxides         and amines, preferably amines, more preferably monoethanolamine,         triethanolamine, tridecylamine.

The present invention further provides aqueous systems, for example water/oil mixtures, comprising compounds of the general formula (II), preference being given to the presence of 0.001 to 5% by weight of the compounds of the general formula (II), based on the total amount of all substance in the aqueous system. Such aqueous systems comprising compounds of the general formula (II) preferably additionally comprise phosphoric acid or at least partly neutralized phosphoric acid.

For the at least partial neutralization with a base in such aqueous systems or water/oil emulsions comprising compounds of the general formula (II), preference is given to using alkali metal hydroxides, amines, preferably amines, more preferably monoethanolamine, triethanolamine, tridecylamine.

In one embodiment, the aqueous systems, for example water/oil mixtures, comprising compounds of the general formula (II) further comprise acids or at least partly neutralized acids. These acids or at least partly neutralized acids are preferably selected from formic acid, amidosulfonic acid, acetic acid, glycolic acid, methanesulfonic acid, lactic acid, oxalic acid, phosphoric acid, nitric acid, hydrochloric acid, sulfuric acid, citric acid, gluconic acid, salicylic acid, carbonic acid.

The present invention further provides a process for inhibiting the corrosion of metals or metal alloys in contact with aqueous systems, for example water/oil mixtures, wherein compounds of the general formula (I) are added to the aqueous system. The amount of the compounds of the general formula (I) used here can vary over a wide range, depending on the conditions in the aqueous system. Preference is given to using from 0.001 to 5% by weight of the compounds of the general formula (I), based on the total amount of all substances in the aqueous system, more preferably from 0.1 to 1% by weight.

The present invention provides corrosion inhibitors, the use of which in processes for inhibiting the corrosion of metals or metal alloys is substantially independent of the boundary conditions such as the pH or the specific composition of the metal. In addition, corrosion by acids is prevented or suppressed by the inventive use of the compounds of the general formula (I) substantially irrespective of the type of acid.

The invention is illustrated in detail by the examples without any restriction of the subject matter of the invention by the examples.

EXAMPLES

The pH was measured with the aid of a pH meter with an electrode.

Example 1 General Method for Preparation of the Compounds of the General Formula (I)

The compounds of the general formula (I) or (II) are obtainable with the aid of the Schotten-Baumann reaction and were generally prepared by the method which follows.

First of all, an amine, for example an amino acid, was initially charged in water with stirring. Thereafter, 30% NaOH solution was added until a pH in the range from 10.5 to 11 was established in the reaction solution. The reaction solution was optionally cooled in order that the temperature did not rise above 30° C.

Thereafter, cyanuric chloride (in a molar ratio of about 1:3 relative to the amine, preferably with an about 10% excess of amine over and above this), dissolved in tetrahydrofuran, with stirring, was added dropwise to the reaction solution within 1 to 2 hours. The reaction solution was optionally cooled in order that the temperature did not rise above 30° C. In the course of this, the pH of the reaction solution was kept within the range from 10.5 to 11 by further addition of 30% NaOH solution while stirring.

After complete addition of the cyanuric chloride, the reaction solution was heated to 60° C. and the pH of the reaction solution was kept within the range from 10.5 to 11 by further addition of 30% NaOH solution while stirring.

The further conversion in the reaction solution was monitored until, generally overnight, a constant pH in the reaction solution was established.

Thereafter, according to the properties of the reaction product after the reaction, different isolation and purification steps were effected.

The workup was effected by dropwise addition of concentrated hydrochloric acid (32-36%) down to pH 1 with control of the temperature at 20-25° C.

-   -   a) Product had precipitated: the product was isolated from the         reaction solution by filtering off with suction or filtering,         then washing with water and drying at 60-100° C. in a vacuum         drying cabinet.     -   b) Product was dissolved in the organic phase (biphasic system:         water/organic solvent), preferably with ethyl acetate or         dichloromethane. The product was removed with the aid of a         separating funnel, washed with water and dried, and concentrated         on a rotary evaporator at 60-70° C. with suitable vacuum.     -   c) Product was insoluble in the organic phase but soluble in         water: the reaction solution was concentrated to constant weight         on a rotary evaporator. Thereafter, the product was repeatedly         (typically three times) dissolved hot (at 90° C.) with acetic         acid or DMF and then filtered off with suction or filtered. This         leaves sodium chloride and the resulting mother liquor is         concentrated in a rotary evaporator and dried to constant weight         in a vacuum drying cabinet.

The compounds of the general formula (I) or (II) which were obtained as products of the above-described reaction were able to be at least partly neutralized in a further step with the aid of a base, for example triethanolamine.

For this purpose, the product, water and the base were mixed with one another and stirred at approx. 70° C. for about 1 to 2 hours. If the solution was turbid, it was clarified by filtration. After checking the pH, further base was added if necessary until a constant pH, for example about pH=8.3 in the case of triethanolamine, was established.

The following compounds and table 1 show a summary of the compounds of the general formula (I) or (II) obtained:

TABLE 1 C. Yield g/% of No. Compound Solvent Reactants Form/color theory Analysis 1 C1 water, THF cyanuric white solid BP: 14.9 g, 50% NCHCI-EA, chloride, >250° C. LC/MS, IR glycine 2 C1 water, THF cyanuric white solid 160 g IR, LC/MS chloride, glycine 3 C2 water, THF cyanuric white solid/BP: 20.18 g, 60% NCHCI- chloride, 211° C. EA, H NMR, sarcosine IR, LC/MS, DC 4 C2 water, THF cyanuric white solid 16.3 g, 95% DC, IR, chloride, H NMR sarcosine 5 C3 water C1, slightly reddish, LC/MS triethanolamine clear solution 6 C3 water C1, yellow clear none triethanolamine solution 7 C4 water C2, TEA yellowish oil none 8 C4 water C2, TEA yellowish oil none 9 C5 water, THF cyanuric white solid 201.1 g, 85% IR, H NMR chloride, aspartic acid 10 C6 water C5 reddish solution none 11 C7 water, THF cyanuric white solid 70%, after a IR, LC/MS, chloride, second H NMR, CI- glutamic acid extraction with EA DMF: 38% 12 C8 water, THF cyanuric whitish-yellow solid 53.5 g, 86.5% IR, LC/MS, chloride, H NMR, CI- tyrosine EA, 13 C8 water, THF cyanuric yellowish solid 44.1 g, 71% IR, LC/MS, chloride, H NMR, CI- tyrosine EA 14 C9 water, THF cyanuric white foam 50.5 g, 97% IR, LC/MS, chloride, H NMR, S-N- methionine EA, DC 15 C9 water, THF cyanuric white foam 155.6 g, IR, H NMR chloride, 100% methionine 16 C10 water C9, TEA, pale yellow clear none demin. water solution 17 C10 water C9, TEA, pale yellow clear none demin. water solution 18 C11 water, THF lysine, cyanuric yellowish solid 25.1 g, 49% IR, LC/MS, chloride, EA: CI, MAL- DI MS 19 C12 water, THF cyanuric whitish solid 52.8 g, 92% IR, LC/MS, CI chloride, analysis, phenylalanine H NMR 20 C13 water, THF cyanuric clear yellow 75.7 g, 96.2% LC/MS, chloride, viscous oil H NMR thiolactic acid 21 C14 water, THF C13, clear, pale yellow triethanolamine slightly viscous solution

In addition, the following compounds of the general formula (I) or (II) or salts thereof with triethanolamine were prepared:

For the preparation, commercially available compound C′

was dried at 100° C. to constant weight in a vacuum drying cabinet. 46.9 g (1 eq) of dried C′ were suspended in 400 ml of toluene. At 20° C., 53.6 g (4.50 eq) of thionyl chloride were added dropwise within 30 minutes. The reaction mixture was heated to 60° C. within one hour and then kept at 60° C. for one hour. During the reaction, evolution of gas became visible. A clear yellow solution was obtained. Subsequent, the reaction mixture was heated and kept at 70° C. for one hour. After cooling, the reaction mixture was concentrated to constant weight after approx. 3.5 h in a rotary evaporator at 70° C. and 40 mbar. Subsequently, post-drying was conducted under high vacuum at 80° C. for 2 hours. 60 g of a clear brown viscous oil were obtained.

The oil was dissolved in 150 ml of THF abs at 60° C. and 3.5 h. 125 g of a 40% sarcosine sodium salt solution were adjusted to pH 10.9-11.1 with 50% sodium hydroxide solution in a four-neck flask with good stirring. The acid chloride solution in THF was added dropwise within 1 h and, at the same time, the pH was kept within the range of 10.9-11.1 with 50% sodium hydroxide solution and the temperature was kept below 30° C. At 30° C., reaction was subsequently completed for 2 h and the pH was still kept at approximately 11.0. This gave rise to a clear brown solution. With good stirring and ice cooling, the reaction mixture was adjusted to pH 1 with concentrated hydrochloric acid. On a rotary evaporator, the THF was distilled off at 60° C. and 200 mbar.

In a separating funnel, 200 ml of ethyl acetate:ethanol were added to the resulting oil phase and turbid aqueous phases. The organic phase was washed 3 times with 50 ml of brine and twice with 50 ml of water and then concentrated in a rotary evaporator at 70° C. and 30-60 mbar to constant weight after approx. 4 h. 75 g of a highly viscous, clear oil were obtained.

In a round-bottom flask, 47 g of triethanolamine were added to 75 g of the acid obtained. The mixture was stirred at 70° C. for 2 h. The resulting clear dark brown solution with a little sediment was decanted off and diluted with 122 g of water. The resulting solution had a pH of 7.5.

A 1 l four-neck flask is initially charged with 50.55 g (1 eq.) of melamine and 423.54 g (12 eq.) of ethylene carbonate, and the mixture was heated to 170° C. while stirring within 2 h. After 1.5 h at 170° C., no further CO2 was formed; the experiment continued at 170° C. for another 1 h.

Ethylene carbonate was used as a synthon of ethylene oxide in the ethoxylation of melamine, as described in WO09144274A2 or DE102009026575A1. The melamine is typically ethoxylated to give a tertiary amine; secondary amines or carbamate linkages can form in a small proportion.

A 2 l metal reactor was initially charged with 240 g of the ethoxylated melamine and 2.48 g of potassium tert-butoxide at 40° C. The reactor was purged with nitrogen. Under 1.5 bar of nitrogen, with stirring at 100 rpm and after heating to 130° C., 255 g (12 eq) of propylene oxide were metered in in portions over the course of 225 min (50 g in the first 15 min, 205 g in the remaining 205 min). The stirrer was increased to 200 rpm within 5 min. The experiment was stirred at 130° C. for a further 10 hours, and then cooled to 80° C.

67.4 g of the alkoxylated melamine formed were initially charged and heated to 40° C. 37.3 g of polyphosphoric acid were added dropwise within 35 min. In the course of this, the temperature rises to 63° C. The reaction mixture was then heated to 90° C., kept at 90° C. for a further 4 hours and reacted to completion at 70° C. for 2 hours.

104.65 g of the phosphated/alkoxylated melamine were neutralized in a round-bottom flask by dropwise addition of 67.1 g (9 eq) of triethanolamine (TEA). The first 6 eq were added dropwise at 90° C. within 30 min; the reaction mixture was stirred at 90° C. for a further 30 min. The remaining amount of triethanolamine was added dropwise within 15 min; the reaction mixture subsequently reacted for a further 30 min.

Example 2

Corrosion tests were conducted with the aid of the method according to ASTM G31-72.

The contact temperature was 23° C.

The contact time was 24 hours.

The area of the steel sheet (coupons) was 21.4 cm². The coupons had the dimensions of 5 cm×2 cm×0.1 cm. This gives rise to an area of 21.4 cm²:

In the case of use of compound C15, the following values were obtained in the corrosion test (cf. table 2).

TABLE 2 Material removal Corrosive medium Steel type Inhibitor conc. rate mm/a Formic acid 30% 1.0037 0.00% 4.11 Formic acid 30% 1.0037 1.00% 0.04 Amidosulfonic acid 15% 1.0037 0.00% 26.80 Amidosulfonic add 15% 1.0037 1.00% 0.08 Phosphoric acid 30% 1.0037 0.00% 51.50 Phosphoric acid 30% 1.0037 1.00% 0.13 Hydrochloric acid 10% 1.0037 0.00% 22.07 Hydrochloric acid 10% 1.0037 1.00% 0.81 Sulfuric acid 30% 1.0037 0.00% 167.00 Sulfuric acid 30% 1.0037 1.00% 0.64

The material removal rate as a measure of corrosion is distinctly reduced in the case of use of the inhibitor.

The inhibitor concentration is the concentration of C15 in % by weight based on the total amount of the corrosive medium and C15.

Steel type 1.0037 is the materials no. according to DIN. This is iron with the following secondary components:

C: max. 0.17% Mn: max 1.4% P: max. 0.045% S: max. 0.045% N: max. 0.009%

The density is 7.85 g/cm³.

The material removal rate in the unit of millimeters per year is then calculated by the following formula:

Material removal rate [mm/a]=(weight loss [g]*K)/(density [g/cm³]*area [cm²]*contact time [h])

K: 8.76*10⁴ 

1. A process for inhibiting corrosion of metals or metal alloys in contact with an aqueous system, the process comprising adding to the aqueous system a compound of formula (I):

wherein A¹, A², and A³ are each independently N—R¹¹, N—R¹², N—R¹³, S, or O, R¹¹, R¹², and R³ are each independently H, C₁-C₂₀-alkyl, or C₃-C₁₅-cycloalkyl, X¹², X²², and X³² are each independently (X-a) to (X-m) groups

* is a bond to A¹, A² or A³, ** is a bond to Y¹², Y²² or Y³², R⁴ is the same or different and is independently H, or CH₃, R⁵ is a side chain of a natural alpha-amino acid, Y¹², Y²², and Y³² are each independently carboxylate, phosphate, phosphonate, sulfonate, or a quaternary ammonium group, X¹²-Y¹², X²²-Y²², and X³²-Y³² may be the same or different and may each independently also together be O—H, n and m, are each independently an integer of from 1 to 20, p is an integer of from 1 to 30, or a salt thereof, obtained, by at least partial neutralization with a base selected from the group consisting of an alkali metal hydroxide and an amine, wherein either R¹¹, R¹² and R¹³ may each be interrupted at any position by a heteroatom, in which a number of heteroatoms is not more than 10, R¹¹, R¹² and R¹³ and/or may each be substituted at any position, but not more than five times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, in which these may likewise be substituted not more than twice by a group thereof, or both.
 2. The process according to claim 1, wherein of from 0.001 to 5% by weight of the compound of formula (I), based on a total amount of all substances in the aqueous system, is present.
 3. The process according to claim 1, comprising inhibiting corrosion of metals or metal alloys in the field of cleaning compositions, cooling fluids, oilfield chemicals, electronics chemicals or lubricants.
 4. The process according to claim 1, wherein the metals or metal alloys comprise iron.
 5. The process according to claim 4, wherein the metals or metal alloys comprise chromium, nickel, molybdenum, aluminum, copper, zinc, or a mixture thereof.
 6. A compound of formula (II):

wherein A⁴, A⁵, and A⁶ are each independently N—R⁴¹, N—R⁵¹, N—R⁶¹, or O, R⁴¹, R⁵¹, and R⁶¹ are each independently H, C₁-C₂₀-alkyl, or C₃-C₁₀-cycloalkyl, X⁴², X⁵², and X⁶² are each independently (X-a′) to (X-m′) groups

* is a bond to A⁴, A⁵ or A⁶, ** is a bond to Y⁴², Y⁵² or Y⁶², R⁶ is the same or different and is independently H, or CH₃, R⁷ is a side chain of a natural alpha-amino acid, Y⁴², Y⁵², and Y⁶² are each independently carboxylate, phosphate, phosphonate, sulfonate, or a quaternary ammonium group, X⁴²-Y⁴², X⁵²-Y⁵², and X⁶²-Y⁶² may be the same or different and may each independently also together be O—H, q and r, are each independently an integer of from 1 to 20, and s is an integer of from 1 to 30, or a salt of the compound of formula (II), obtained by at least partial neutralization with a base selected from the group consisting of an alkali metal hydroxide and an amine, wherein either substituents R⁴¹, R⁵¹ and R⁶¹ may each be interrupted at any position by a heteroatom, in which a number of these heteroatoms is not more than 10, R⁴¹, R⁵¹, and R⁶¹ may each be substituted at any position, but not more than five times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, wherein these may likewise be substituted not more than twice by a group thereof, or both.
 7. An aqueous system comprising the compound according to claim
 6. 8. The aqueous system according to claim 7, comprising of from 0.001 to 5% by weight of the compound of formula (II), based on a total amount of all substances in the aqueous system.
 9. The aqueous system according to claim 7, further comprising phosphoric acid or at least partly neutralized phosphoric acid.
 10. The aqueous system according to claim 7, wherein the at least partial neutralization is effected with a base selected from the group consisting of an alkali metal hydroxide and an amine.
 11. The aqueous system according to claim 7, further comprising an acid or an at least partly neutralized acid.
 12. The aqueous system according to claim 11, wherein the acid is selected from the group consisting of formic acid, amidosulfonic acid, acetic acid, glycolic acid, methanesulfonic acid, lactic acid, oxalic acid, phosphoric acid, nitric acid, hydrochloric acid, sulfuric acid, citric acid, gluconic acid, salicylic acid, and carbonic acid. 13-14. (canceled)
 15. The process according to claim 1, wherein R¹¹, R¹² and R¹³ may each be interrupted at any position by a heteroatom, in which a number of heteroatoms is not more than
 10. 16. The process according to claim 1, wherein R¹¹, R¹² and R¹³ may each be substituted at any position, but not more than five times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, in which these may likewise be substituted not more than twice by a group thereof.
 17. The process according to claim 1, wherein R¹¹, R¹² and R¹³ may each be interrupted at any position by a heteroatom, in which a number of heteroatoms is not more than 10, and R¹¹, R¹² and R¹³ may each be substituted at any position, but not more than five times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, in which these may likewise be substituted not more than twice by a group thereof.
 18. The process according to claim 1, wherein either R¹¹, R¹² and R¹³ may each be interrupted at any position by a heteroatom, in which a number of heteroatoms is not more than 8, R¹¹, R¹² and R¹³ may each be substituted at any position, but not more than four times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, in which these may likewise be substituted not more than twice by a group thereof, or both.
 19. The process according to claim 1, wherein either R¹¹, R¹² and R¹³ may each be interrupted at any position by a heteroatom, in which a number of heteroatoms is not more than 5, R¹¹, R¹² and R¹³ may each be substituted at any position, but not more than three times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, in which these may likewise be substituted not more than twice by a group thereof, or both.
 20. The process according to claim 1, wherein either R¹¹, R¹² and R¹³ may each be interrupted at any position by a heteroatom, in which a number of heteroatoms is not more than 3, R¹¹, R¹² and R¹³ may each be substituted at any position, but not more than three times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, in which these may likewise be substituted not more than once by a group thereof, or both.
 21. The compound according to claim 6, or a salt thereof, wherein R⁴¹, R⁵¹ and R⁶¹ may each be interrupted at any position by a heteroatom, in which a number of these heteroatoms is not more than 10
 22. The compound according to claim 6, or a salt thereof, wherein R⁴¹, R⁵¹, and R⁶¹ may each be substituted at any position, but not more than five times, by C₁-C₁₀-alkyl, OH, CO₂H, PO(OH), PO(OH)₂, SO₂H or SO₃H, wherein these may likewise be substituted not more than twice by a group thereof. 